Known mobile communications systems, such as the Mobitex™ and DataTAC™ mobile communications system in North America, may include hundreds of base stations that provide cellular coverage for mobile communications devices. Since the coverage area for any base station is typically limited by factors such as base station power levels and environmental conditions, a communications device may have to establish communications via different base stations as it moves within the mobile communication network. This process of switching base stations is generally referred to as “roaming.”
Various methods are known for controlling when a mobile communications device will roam from one base station to another. For example, in one typical roaming method, a mobile communications device monitors the signal strength of surrounding base stations in order to calculate a received signal strength indicator (RSSI) for the current and one or more adjacent base stations. The RSSI value of a current base station is then compared with the RSSI values of one or more adjacent base stations to identify possible roam candidate base stations. An adjacent base station, for example the adjacent base station with the highest RSSI value that is at least a certain threshold amount greater than the RSSI value of the current base station, may be selected as a roam candidate. The RSSI value of a roam candidate base station is typically compared with a pre-selected minimum threshold RSSI value, and if the RSSI of the roam candidate base station is greater than this threshold, then the mobile communications device roams to the roam candidate base station. However, this roaming method is inefficient, for example, in fleet distribution situations in which multiple base stations cover a large cluster of co-located mobile communications devices. In such situations, the fleet of mobile communications devices will typically gravitate towards the base station with the strongest RSSI, potentially overloading that base station and leaving other base stations under-utilized.